U.S. Pat. No. 3,825,364 shows an outer wall which is completely porous in form. A cavity is present between this supporting wall and a substrate.
U.S. Pat. No. 5,080,557 shows a layer structure comprising a substrate, a porous interlayer and an absolutely impervious outer layer.
U.S. Pat. No. 4,318,666, compared to U.S. Pat. No. 5,080,557, shows additional cooling passages in the substrate, to which a porous interlayer and an impervious outer layer have been applied.
JP 10-231 704 shows a substrate with cooling passages and a porous interlayer.
WO03/006883 and U.S. Pat. No. 6,412,541 show a porous structure within a supporting wall, the wall once again having a coating on the outer side. The wall and the coating have cooling passages.
However, the layer structures are inadequately cooled.